1. Field of the Invention
The invention relates generally to the field of semiconductor fabrication processes. More specifically, the invention relates to an electromagnetic wave irradiation apparatus and a method to bond voids or unbonded areas at the interface of a bonded pair of substrates, which are common defects that may occur in a substrate bonding process. The invention likewise relates to substrate bonding and the downstream manufacturing of electronic and photonic devices.
2. Prior Art
Direct substrate bonding generally refers to a semiconductor process wherein the planar surfaces of chemical-mechanical planarized (“CMP”), smooth and clean substrates of almost any material are brought into contact at room temperature and are locally attracted to each other by a van der Waals force and/or hydrogen bonding force and adhere or bond to each other. Substrate bonding of this type may be known in the semiconductor processing arts as “direct bonding”, or “cold welding”.
Generally, substrates in a bonding process are semiconductor substrates or wafers consisting of single crystal materials such as silicon, gallium nitride or gallium arsenide as are commonly used in microelectronics or optoelectronics. Unfortunately, bonded substrates that use van der Waals force and/or hydrogen bonding force at room temperature have a bond that is undesirably weak compared to that of covalently- or ionically-bonded materials.
In most direct bonding operations performed at wafer-level for fabrication of micro-electromechanical systems (MEMS), nano-electromechanical systems (NEMS), microelectronics and optoelectronics, surface treatments (e.g., surface planarization, hydration, plasma activation) are conducted prior to substrate surface contact to promote surface attraction and the bonding process. Typically, direct bonding is assisted by compressing the two substrate surfaces together during a direct bonding process. Also, it is not uncommon that one of the two bonded substrates, or both, are back-thinned to a thickness that, depending on the specific application, may be in the range of a few microns (μm) down to a few nanometers (nm).
Unfortunately, the current state of the art in substrate bonding undesirably results in unbonded areas or bond voids that are introduced or formed at the interface of the substrate active surfaces. These unbonded areas (or voids) may be the result of unwanted particles or contaminants from etching systems, implantations, chemical vapor deposition (CVD), and/or CMP steps or any number of processes. Defective photolithography steps may also result in surface defects, the locations of which remain unbonded at the substrate bond interface. It is vitally important to minimize or preferably eliminate all unbonded regions and bond voids at the substrate/wafer-bonding interface since such unbonded areas may ultimately lead to device failure and low wafer yield.
The invention and its various embodiments can now be better understood by turning to the following description of the embodiments which are presented as illustrated examples of the invention in any subsequent claims in any application claiming priority to this application. It is expressly understood that the invention as defined by such claims may be broader than the illustrated embodiments described below.